Microfibrils, 10-14 nm in diameter, are extracellular matrix proteins which play important roles in the assembly and maintenance of elastic fibers..sup.1.2 A bovine microfibril-associated glycoprotein (MAGP) with MW 31 kDa was discovered in 1986,.sup.3,4 and then cloned in 1994..sup.5 Kobayashi et al. Reported a bovine MAGP-36 with calcium-binding and fibrinogen-like domains, with a tissue distribution uniquely limited to aorta..sup.6 A human MAGP, implicated to Smith Magenis syndrome, was sequenced in 1995..sup.7
Immunoglobulin (IgG) purified from the aortic wall of patients with abdominal aortic aneurysms (AAAs) is immunoreactive with a human aortic protein that is homologous to MAGP-36..sup.8 As described herein, the protein has been purified and partially sequenced. It has vitronectin and fibrinogen-like domains, along with a putative calcium-binding domain..sup.9 It is designated Aortic Aneurysm-Autoantigenic Protein-40 kDa or Aortic-Aneurysm-Associated Protein-40 (AAAP-40)..sup.9
Another matrix protein detected in human embryonic tissue (sulfated protein 30 kDa=SP-30) has been reported to be immunoreactive with monoclonal antibodies against human vitronectin, and it co-distributes in tissue with the protein that is immunoreactive with antibody against MAGP-31. A sequence in AAAP-40 matches residues #230-240 in human vitronectin. It was demonstrated that AAAP-40 was immunoreactive with rabbit anti-human vitronectin antibody. In addition, the experiments described in this application were carried out to clone the cDNA encoding AAAP-40, express it as a recombinant, and assign it conclusively as a human MAGP.
Nomenclature of the microfibrillar proteins associated with the elastin fiber is confusing. A principal component of the microfibril is fibrillin (fib-15), discovered by Sakai, et al.,.sup.1 and Marfan's syndrome has been traced to mutations in the gene for fibrillin on chromosome 15..sup.2 3 4 A bovine microfibrillar protein (Mr apx. 31 kDa) was discovered in 1986 by Gibson, et al.,.sup.5 6 who coined the term "microfibril-associated glycoprotein" (MAGP). Bashir, et al. have also cloned the gene for this protein..sup.7 Kobayashi, et al. reported a 36 kDa calcium-binding protein, also in cow, with tissue distribution uniquely limited to the aorta (MAGP-36)..sup.8 The second human MAGP (deduced MW 21 kDa) was recently reported to have an open reading frame of 255 amino acids and to be linked to Smith Magenis syndrome. .sup.9 The authors of the paper describing the Smith Magenis protein prefer the abbreviation "MFAP", to avoid confusion with abbreviations for microfilamentous proteins.
It has been reported that IgG from the aortic wall of patients with abdominal aortic aneurysms (AAA) is immunoreactive with a human aortic protein (MW apx. 80 kDa) that has features of the bovine aortic protein of Kobayshi, et al. (MAGP-36)..sup.10 MAGP-36 occurs in nature as a disulfide-bonded dimer, so further tissue extractions under reducing conditions as described by Prosser, et al. were carried out as described herein..sup.11 This approach has led to the partial characterization of a protein of apx. 40 kDa that is immunoreactive with AAA IgG. This protein is called Aortic Aneurysm-Autoantigenic Protein-40 kDa or Aortic-Aneurysm-Associated Protein-40 (AAAP-40). The present application describes its partial sequence and suggests that, since it is the third human microfibrillar protein to be described, it be called MAGP-3.